The present invention relates to a technology for performing a stable data write operation at a low operating ambient temperature within a magnetic recording apparatus that employs a load/unload design, and more particularly to a technology for completing a stable data write operation within a short period of time at a low operating ambient temperature.
The magnetic head for use in a magnetic disk drive, which is a typical magnetic recording apparatus, is formed at the end of a slider, which is made of an Al—Ti—C sintered body, by using a thin-film process. A combination of the magnetic head and slider is hereinafter referred to as the head/slider assembly. An air-bearing surface (hereinafter referred to as the ABS) is formed on a magnetic disk surface that faces the head/slider assembly. When a viscous airstream, which is generated over a rotating magnetic disk, passes through a gap between the ABS and magnetic disk surface, the ABS receives buoyancy. The head/slider assembly is then thrust upward from the magnetic disk surface and placed at a position where the buoyancy is in balance with the pressure load of a slider-supporting head gimbal assembly (hereinafter referred to as the HGA). As a result, a gap within a predetermined range is maintained between the magnetic head and magnetic disk magnetic layer while the magnetic disk rotates. To permit the magnetic head to perform a stable write operation on the magnetic layer, it is necessary that the gap between the magnetic head and magnetic layer be maintained within the predetermined range.
If the magnetic head is positioned too close to the magnetic layer, the head/slider assembly may come into contact with the magnetic disk surface, thereby damaging the magnetic disk and magnetic head. If, on the contrary, there is an excessive gap between the magnetic head and magnetic layer, an unstable data write operation results due to reduced magnetic coupling between the magnetic head and magnetic layer. The magnetic head generally comprises an inductive write head and a GMR or MR read head. The inductive write head comprises a coil, a magnetic pole piece, and a write gap. The GMR read head uses a giant magnetoresistive element, whereas the MR read head uses a magnetoresistive element.
When a write current flows to the write head for the purpose of writing data onto the magnetic disk, heat is generated due to resistance that is provided by a write head coil. This raises the ambient temperature of the coil. In this instance, thermal protrusion occurs due to a thermal expansion coefficient difference between the materials of the write head and slider main body. In thermal protrusion, a write gap section, which is formed by the write head magnetic pole piece, protrudes from the ABS. Even if the gap between the head/slider assembly and magnetic disk surface remains unchanged, thermal protrusion (hereinafter referred to as thermal expansion) varies the gap between the write head and magnetic layer to the detriment of write operation stability.
The technology disclosed by Patent Document 1 (Japanese Patent Laid-Open No. 79126/2004) provides a magnetic disk drive that not only reduces a read error occurring at a low temperature, but also enlarges the operating temperature range while maintaining high reliability and high stability by avoiding a head/media crash, which may occur between the magnetic head and magnetic disk of a magnetic disk drive having an increased recording density. The technology disclosed by this document also moves the magnetic head to its unloading position temporarily before performing an advance pseudo-write operation.
In recent years, the gap between the magnetic head and magnetic disk has decreased in addition to an increase in the magnetic disk recording density. Consequently, the recording performance has been greatly influenced by a change in the gap between the head/slider assembly and magnetic layer. In this specification, the gap between the write head and rotating magnetic disk surface is hereinafter referred to as the fly height. Thermal protrusion, which is generated by Joule heat when a write current flows to the write head coil, decreases the fly height prevailing after the write head temperature is raised by a write operation continuously performed for a specified period of time, to a level lower than the fly height prevailing while the write head temperature is low immediately after the beginning of a write operation.
While the magnetic disk is rotating, it is necessary to prevent the write head from coming into contact with the magnetic disk wherever possible. Therefore, the ABS and HGA parameters related to the fly height are determined with reference to a low fly height that prevails when the write head temperature is raised. However, the write head may not be able to magnetize the magnetic layer with an adequate magnetic field strength due to an increased gap between the write head and magnetic layer because the fly height is increased before thermal protrusion. When, in reality, a write command and user data were received from a host computer and written onto the magnetic disk, it was found that the soft error rate (hereinafter referred to as the SER) of approximately 20 leading data sectors into which the user data was written, including a sector containing a first address, was higher than in the subsequent data sectors.
In a magnetic disk drive that employs the load/unload design, the magnetic disk rotation is stopped in a power supply stop mode or standby mode with the write head unloaded onto the ramp. If the operating ambient temperature of the magnetic disk drive is low, the write head temperature decreases while the write head is unloaded onto the ramp, thereby increasing the fly height for the next write operation. Therefore, if a write command is received to start a write operation after the write head is unloaded onto the ramp, a stable data write operation may not always be performed.